Importance

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Abstract

An optical sheet to be used for a back light unit of a liquid crystal display having at least a lamp and a light guiding plate has the following structure. The optical sheet is constituted by a lower base portion and an upper fitting portion which are fitted each other in a vertical direction with less margin, and the base portion and the fitting portion are formed of materials having different refractive indices. The base portion is provided with a large number of triangular portions having a triangular sectional shape in parallel, the triangular portion having a first side surface positioned on the left side and a second side surface positioned on the right side. Moreover, the first side surface of the triangular portion has an angle which is equal to or greater than an angle formed between a direction taking a peak of a ray refracted and incident on an inside of the base portion through a light guiding plate and the transverse direction. Furthermore, a direction taking a peak of a ray refracted and incident on the fitting portion through the second side surface of the base portion is caused to more approach a just upward direction than a direction taking a peak of a ray transmitted to the second side surface through the inside of the base portion.

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First Claim